Limited information exists in the literature regarding the copolymerization of vinyl ethylene carbonate (VEC), especially the formation of emulsion copolymers incorporating VEC. xe2x80x9cSynthesis of cyclic carbonate functional polymers,xe2x80x9d by Dean C. Webster and Allen L. Crain, ACS Symposium Series 704, American Chemical Society, 1998, Chapter 21, pages 303 to 320, contains a review of VEC copolymerization. Emulsion copolymerization of VEC with vinyl acetate and butyl acrylate is reported. Up to 15% VEC was incorporated into vinyl acetate/butyl acrylate latexes containing 20% butyl acrylate and 65 to 78% vinyl acetate.
U.S. Pat. No. 2,511,942 (Prichard, 1950) discloses the preparation of VEC and indicates that it can be copolymerized with other unsaturated monomers, such as ethylene, isobutylene, styrene, vinyl chloride, vinyl acetate, and vinyl acrylics. Emulsion copolymerization is not disclosed.
xe2x80x9cPolymerization of vinyl ethylene carbonate and reaction of the formed polymer,xe2x80x9d by Teruzo Asahara, et al. (Production Research, Vol.25, No. 7, 1973), discloses free radical polymerization of VEC with each of styrene, vinyl acetate, and maleic anhydride.
U.S. Pat. No. 5,567,527 (Webster et al., 1996) discloses carbonate functional copolymers formed from the free-radical copolymerization of VEC with other ethylenically unsaturated monomers such as acrylic and methacrylic acids and their esters, styrene-type monomers, vinyl chloride, vinyl acetate, allyl compounds, and acrylamide. The copolymers can be crosslinked with multifunctional primary amines and are reported to be useful in two-component crosslinked or thermosetting organic coatings. Emulsion copolymers are formed in the presence of surfactants and comprise water and a curable acrylic copolymer containing 1 to 50 wt % VEC, based on the total weight of monomers. An example shows the formation of an emulsion copolymer of VEC with vinyl acetate and butyl acrylate.
WO 99/62970 (Webster et al., 1999) discloses a process for the free radical copolymerization of VEC with other unsaturated monomers. Examples show the emulsion polymerization of VEC with vinyl acetate and butyl acrylate to form copolymers in which the ratio of VEC to other monomers is 25:75.
U.S. Pat. No. 4,263,418 (Steffen et al., 1981) discloses graft copolymers consisting of 10 to 80 wt % ethylene/vinyl ester copolymer containing 1 to 75 wt % vinyl ester; and 90 to 20 wt % of a grafted monomer mixture consisting essentially of: 5 to 50 wt % acrylonitrile and/or methacrylonitrile; 95 to 50 wt % of one or more aromatic monovinyl compound; and small quantities (0.01 to 0.5% by weight) of copolymerized allyl compound, such as VEC or diallyl carbonate.
WO 99/62968 (Mackenzie, et al., 1999) discloses supported group 8-10 transition metal olefin polymerization catalysts. Solution polymerization of 96.5 to 95.5 wt % ethylene and 3.5 to 4.5 wt % VEC is shown in examples 77 and 78.
This invention is directed to aqueous based emulsion copolymers containing vinyl ethylene carbonate (VEC), ethylene and at least one other ethylenically unsaturated monomer. One embodiment of this invention is the incorporation of VEC into vinyl acetate-ethylene emulsion copolymers. Another embodiment is aqueous based poly(vinyl alcohol)-containing emulsion copolymers that are formed by copolymerizing VEC with vinyl acetate and, optionally, another ethylenically unsaturated monomer in the presence of poly(vinyl alcohol). The aqueous based poly(vinyl alcohol)-containing emulsion copolymer can be a grafted poly(vinyl alcohol) polymer. Yet another embodiment of this invention is the use of emulsion copolymers of VEC and other ethylenically unsaturated monomers such as vinyl acetate or vinyl acrylic compounds in adhesive applications, such as wood glue.
There are several advantages to incorporating VEC into emulsion copolymers. For example:
the emulsion copolymers exhibit good adhesive properties;
the Tg (glass transition temperature) of the emulsion copolymer can be increased;
a two stage emulsion polymerization can be used to produce VEC-vinyl acetate-ethylene emulsion copolymers with a high ethylene content; and
incorporation of other ethylenically unsaturated monomers into poly(vinyl alcohol)-containing polymers, can be enhanced.
The VEC emulsion copolymers of this invention can be used in a variety of applications, such as adhesives, coatings, and nonwovens and paper applications.
VEC can be emulsion copolymerized with vinyl acetate and a variety of other ethylenically unsaturated monomers using standard emulsion polymerization procedures as practiced in the industry.
The emulsion copolymers comprise 2 to 30 wt % of VEC, 2 to 50 wt % ethylene, and 20 to 96 wt % of one or more additional ethylenically unsaturated copolymerizable monomer, based on the total monomers.
Suitable ethylenically unsaturated monomers which can be employed for emulsion copolymerization with VEC and ethylene include, but are not limited to, vinyl acetate, vinyl chloride, C1 to C12 alkyl acrylates, and C1 to C12 alkyl methacrylates, such as ethyl methacrylate, methyl methacrylate, 2-ethylhexyl acrylate, butyl acrylate, propyl acrylate, ethyl acrylate, methyl acrylate, hydroxyethyl acrylate, and hydroxypropyl acrylate, and mixtures thereof.
It has been found that ethylene cannot be emulsion copolymerized with VEC in the absence of another ethylenically saturated monomer such as vinyl acetate. It has also been found that incorporation of ethylene is retarded in the preparation of copolymer of ethylene with VEC and another ethylenically unsaturated monomer, using typical emulsion polymerization techniques. However, unexpectedly it has been found that use of a two stage polymerization process is effective in making copolymers containing the amounts of monomers described above.
In the two stage emulsion polymerization, about 30 to 70% of the total monomers (containing about 50% of an ethylenically unsaturated other than ethylene or VEC, and about 50% ethylene) can be reacted in one stage and about 70 to 30% of the total monomers (containing about 30% VEC and about 70% of the other ethylenically unsaturated monomer) can be reacted in another stage using well known emulsion polymerization methods. Specifically, about 15 to 35 wt % vinyl acetate and about 15 to 35 wt % ethylene, based on total amount of monomers, are reacted in the first stage, and about 9 to 21 wt % vinyl ethylene carbonate and 21 to 49 wt % vinyl acetate, based on total amount of monomers, are reacted in the second stage. The order of the above reactions can be reversed, provided that the second reaction is carried out in the presence of the product of the first reaction.
Polymerization can be initiated by thermal initiators or by a redox system. A thermal initiator is typically used at temperatures at or above about 70xc2x0 C. Redox systems are typically used at temperatures below about 70xc2x0 C. The amount of thermal initiator used in the process is 0.1 to 3 wt %, preferably about 0.5 wt %, based on total monomers. Thermal initiators are well known in the emulsion polymer art and include, for example, ammonium persulfate, sodium persulfate, and the like. The amount of oxidizing and reducing agent in the redox system is about 0.1 to 3 wt %. Any suitable redox system known in the art can be used; for example, the reducing agent can be a bisulfite, a sulfoxylate, ascorbic acid, erythorbic acid, and the like. The oxidizing agent can include hydrogen peroxide, organic peroxide such as t-butyl peroxide, persulfates, and the like.
In addition to the above reaction conditions and components, the polymer latex may be stabilized with conventional emulsifiers or surfactants, and protective colloids.
The protective colloid can be poly(vinyl alcohol) in amounts of about 0.5 to 5 wt %, preferably 2 to 5 wt %, based on monomers. The poly(vinyl alcohol) can be 75 to 99+mole % hydrolyzed, preferably 85 to 90 mole % hydrolyzed, with a degree of polymerization ranging from 50 to 3000; preferably, 100 to 1500. The degree of polymerization of the poly(vinyl alcohol) affects the viscosity of the emulsion product; i.e., as degree of polymerization increases, viscosity of the emulsion product increases.
The surfactant or emulsifier can be used at a level of about 1 to 4 wt %, preferably 1.5 to 3 wt %, based on monomers and can include any of the known and conventional surfactants and emulsifying agents, principally the nonionic and anionic materials, heretofore employed in emulsion copolymerization. Among the nonionic surfactants found to provide good results are the Igepal surfactants supplied by Rhone-Poulenc. The Igepal surfactants are members of a series of alkylphenoxy-poly(ethyleneoxy)ethanols having alkyl groups containing from about 7 to 18 carbon atoms, and having from about 4 to 100 ethyleneoxy units, such as the octylphenoxy poly(ethyleneoxy)ethanols, nonylphenoxy poly(ethyleneoxy)ethanols, and dodecylphenoxy poly(ethyleneoxy)ethanols. Other examples of nonionic surfactants include polyoxyalkylene derivatives of hexitol (including sorbitans, sorbides, manitans, and mannides) anhydride, partial long-chain fatty acid esters, such as polyoxyalkylene derivatives of sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate and sorbitan trioleate. Pluronic surfactants L-64 and F-68, supplied by BASF, are examples of other commercial nonionic surfactants which can be used in this invention.
It has been found that VEC emulsion copolymers, such as those described above, are effective in adhesive applications, such as wood glue applications. About 2 wt % to 15 wt % VEC, based on total monomers, can improve the adhesive properties of the emulsion copolymer.
Examples of appropriate wood substrates for wood glue applications include hardboard, particle board, fiberboard, oriented strand board, lauan, plywood, chipboard, veneer, and other timber structures.
A poly(vinyl alcohol)-containing emulsion copolymer can be formed by emulsion copolymerizing VEC, vinyl acetate, and one or more other ethylenically unsaturated monomer in the presence of poly(vinyl alcohol) using known emulsion polymerization techniques, such as those described above. The poly(vinyl alcohol)-containing emulsion copolymer can contain a graft copolymer. Poly(vinyl alcohol)-containing emulsion copolymers of this invention can contain 5 to 30 wt % VEC, 25 to 97 wt % vinyl acetate, 0 to 10 wt % ethylenically unsaturated compound other than VEC and vinyl acetate, and 2 to 35 wt % poly(vinyl alcohol), based on the total weight of all components of the emulsion copolymer. Suitable monomers which can be employed for emulsion copolymerization of vinyl acetate with VEC in the presence poly(vinyl alcohol) include, but are not limited to, ethylene, styrene, vinyl chloride, ethylene, C1 to C12 alkyl acrylates, and C1 to C12 alkyl methacrylates, such as ethyl methacrylate, methyl methacrylate, 2-ethylhexyl acrylate, butyl acrylate, propyl acrylate, ethyl acrylate, methyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, and mixtures thereof. Preferred monomers are ethylene, vinyl chloride, and mixtures thereof.
Other monomers, such as crosslinking monomers, which may be present include, acrylamide, methacrylamide, N-methylolacrylamide, acetoacetoxyethyl methacrylate, maleic acid, alkyl maleate ester, and dialkyl maleate esters, wherein alkyl is C1 to C12.
The poly(vinyl alcohol)-containing emulsion copolymer can be formed by way of a free radical reaction. The free radical copolymerization reaction can be conducted in aqueous media at a temperature necessary to liberate free radicals. Typical temperatures range from 30 to 95xc2x0 C., preferably 40 and 90xc2x0 C.
Total reaction solids levels can vary from 20 to 65 wt %, preferably from 30 to 60 wt %, depending on the molecular weight of the poly(vinyl alcohol).
Examples of free radical initiators that can be employed in the copolymerization reaction are ammonium persulfate, sodium persulfate, potassium persulfate, tert-butylhydroperoxide, and hydrogen peroxide. Approximately 0.1 to 10 wt % (preferably 0.5 to 3 wt %) of the initiator, based on the amount of total monomer is used.
The poly(vinyl alcohol) used in making poly(vinyl alcohol)-containing emulsion copolymers generally has a weight average molecular weight (Mw) ranging from about 5,000 to 300,000, preferably 10,000 to 200,000. Alternatively, the poly(vinyl alcohol) can have a degree of polymerization (Dp) of from 100 to 5,000, preferably 200 to 3500. Poly(vinyl alcohol) is made commercially by the hydrolysis of poly(vinyl acetate) and typically has a hydrolysis level ranging from about 85 to greater than 99 mol %. For free radical emulsion copolymerization, the level of hydrolysis can range from 70 to greater than 99 mol %, preferably 85 to 99 mol % hydrolyzed. Mixed poly(vinyl alcohol) grades, from combinations of poly(vinyl alcohol) polymers which vary in molecular weight and hydrolysis level, can be employed in the polymerization reaction.
The invention will be further clarified by a consideration of the following examples, which are intended to be purely exemplary of the invention.